1. Field of the Invention
The present invention relates to a structure of an aerostatic gas bearing, and more specifically, to an aerostatic gas bearing used as a bearing of a spindle for inspecting a hard disc and executing ultra-precise machining, and the like.
2. Description of the Related Art
Conventionally, many aerostatic gas bearings are in practical use in the form of a gas-feed-restriction-type bearing. The aerostatic gas bearings are classified according to gas-feed restriction types that include an orifice restriction excellent in a load capability achieved by forming pockets in gas-feed holes, an inherent orifice restriction for achieving a restriction effectively by a multiplicity of gas-feed holes, and a surface restriction for realizing an aerostatic gas bearing having a very small clearance.
There is a slot restriction as one of the restriction types that is arranged such that the gas-feed holes of an inherent orifice restriction are slenderly extended in a peripheral direction on a bearing surface so as to change point source gas-feed to line source gas-feed. Since the gas supplied into the bearing flows in an axial direction almost uniformly and does not spread, the bearing has such a feature that the bearing stiffness and the load capacity thereof are increased.
Since the slot restriction has the feature described above, there is proposed a circular slot restriction gas bearing as a gas bearing more excellent in the bearing stiffness and the load capacity.
FIG. 11A is a front sectional view showing an example of a conventional circular slot restriction double-row gas feed bearing, and FIG. 11B is a sectional view of the conventional bearing taken long the line A-Axe2x80x2 of FIG. 11A.
A shaft 43 is inserted through a cylindrical bearing member 44. In the figures, the clearance between the outer peripheral surface of the inserted shaft 43 and the inner peripheral surface of the bearing member 44 is emphasized by showing the clearance in a large size, and the shaft 43 is shown at a decentered position. A fed-gas introduction path 44a is formed in the bearing member 44 to introduce outside gas to both the end surfaces thereof. Ring-shaped shims 41 are clamped between both the end surfaces of the bearing member 44 and slot side plates 45, and the slot side plates 45 are pressed against the shims 41, thereby slot section clearances 42 are formed between the end surfaces of the bearing member 44 and the slot side plates 45, and a slot region 46 that is circular as a whole is formed.
In the gas bearing having the circular slot restrictions as described above has such a structure that the shims having a thickness corresponding to the slot section clearances are clamped between the bearing member and the slot side plates to obtain the slot section clearances. Accordingly, the gas bearing is produced in such a procedure that after the outer and inner peripheries of the bearing member are ground without clamping the shims between the bearing and the slot side plates, the bearing is disassembled, the shims are clamped between the bearing member and the slot side plates 45, and then the bearing is reassembled in order to prevent the slot section clearances from being filled with cuttings. Therefore, the conventional circular slot restriction bearing has a drawback in that a production procedure is complex.
Further, in the circular slot restriction bearing, it is necessary to make the slot section clearances very small to most suitably design the fine clearance region of the bearing where high rigidity can be obtained. However, it is difficult to produce a thin shim.
In addition, further improvement of a restriction effect is limited in the circular slot restriction because gas flows in a peripheral direction.
According to the above arrangement, since a restriction effect is enhanced, the bearing stiffness of the rectangular slots of the present invention can be improved as compared with that of conventional circular slots as well as the load capacity thereof is also improved when maximum rigidity is exerted. Further, an amount of gas flow can be greatly reduced as well as restricting sections can be easily processed.
An object of the present invention is to provide an aerostatic gas bearing capable of easily processing slot sections, improving bearing stiffness and a load capacity, and greatly reducing an amount of gas flow as compared with a conventional circular slot restriction bearing.
In order to accomplish the object of the present invention, an aerostatic gas bearing of a slot restriction type having a clearance formed between the bearing and a shaft and rotatably supporting the shaft by introducing compressed gas from the outside to the clearance through restrictions, includes a cylindrical bearing member having a fed-gas introduction path for introducing external gas and a multiplicity of grooves formed radially on the end surfaces thereof, slot side plates for forming a multiplicity of radial slots between them and the bearing member by being pressed against the end surfaces of the bearing member through the side surfaces thereof, and a casing member accommodating the bearing member and having a gas feed port communicating with the fed-gas introduction path, wherein the restriction effect of the introduced gas is increased by flowing the gas to the outer peripheral surface of the shaft inserted through the bearing member from the multiplicity of radial slots.
In the above arrangement of the present invention, a multiplicity of radial grooves are formed on the end surfaces of the cylindrical bearing member, and slot restrictions are arranged by pressing the slot side plates against the end surfaces of the bearing member.
In the above arrangement of the present invention, a peripheral groove is formed on the outer peripheral surface of the bearing member, the fed-gas introduction path is communicated with the side walls of the peripheral groove, and the slot side plates are fixed by screws from the side walls.
The peripheral groove of the present invention has a depth of several microns to several tens of microns.
Further, the radial slots of the present invention is composed of rectangular slots, the slot side plates is formed in a ring shape, and the casing is composed of a cylindrical casing, respectively.
The outside dimension of the slot side plates of the present invention is slightly smaller than that of the bearing member, and thrust slot clearances are formed between the inner peripheral surface of the casing and the outer peripheral surfaces of the slot side plates.
According to the present invention, thrust plates are fixed on both the end surfaces of the bearing member, and thrust bearing clearances are formed between the thrust plates, and the casing and the slot side plates.
According to the above arrangement, since the restriction effect is enhanced, the bearing stiffness of the rectangular slots are improved as compared with that of circular slots, and the load capacity thereof is also improved when maximum rigidity is exerted. Further, an amount of gas flow can be greatly reduced and restricted sections can be easily processed.